The invention relates to an adjusting device for adjusting the phase position of a shaft, especially a camshaft.
The valves of internal combustion engines, in particular reciprocating internal combustion engines, are actuated by means of camshafts. The camshafts are caused to rotate by a drive shaft or by the crankshaft, via a transmission device. To be able to adapt the opening and closing times of valves to the respective current power output and/or speed of the engine, transmission devices having adjusters for adjusting the phase position of the rotary orientation of the camshafts are used. Such adjusters enable the control times of the intake and/or outlet valves to be influenced according to requirements, so that in particular the so-called overlap of the valve lift curves can be altered. At present, the use of these adjusters for the angle of rotation in the case of the camshafts of the intake valves is preferred. Increasingly, however, the camshafts of the outlet valves are also being rotationally adjusted.
The adjuster is preferably located between the camshaft wheel driven by a chain or a toothed belt and the camshaft. Depending on the respective transmission device, however, another arrangement of the adjuster, for example between the drive shaft and the drive shaft wheel, would also be possible. The relative rotational position between the camshaft wheel and the camshaft can be varied in a predetermined angular range. Preferably, a camshaft rotational range of only 0xc2x0 to 30xc2x0 is sufficient. In the case of four-cycle engines, in which the camshaft rotates at half the speed of the crankshaft, this range corresponds to a crankshaft rotational range of 0xc2x0 to 60xc2x0. If both camshafts are simultaneously adjustable, the term doubly variable camshaft control is used. It produces a fuller engine torque curve and optimizes the preparation of the mixture so that the pollutants in the exhaust gas are reduced.
The object of the adjuster is to adjust the beginning and the end of the valve stroke from xe2x80x9clatexe2x80x9d to xe2x80x9cearlyxe2x80x9d and vice versa by means of the camshaft. This must be achievable over a large speed range of the engine. Preferably, the adjustment should be effected continuously and automatically. The advantages of correct adjustment are: more torque in the lower and middle speed range, less uncombusted residual gases during idling, improved idling, lower pollutant output, internal exhaust gas recycling even at low speed, faster heating up of the catalyst and less raw emission after a cold start, specific functions for adapting the mixture during warm running, reduced fuel consumption and less engine noise.
The invention relates in particular to adjusters which are hydraulically actuated. If required, the adjuster is fed by an additional hydraulic pump. Preferably, however, feeding by the lubricating oil pump of the engine should be sufficient, this being particularly economical and favourable in terms of consumption.
As a result of the valve actuation, the camshaft experiences large torque variations, which the transmission device must withstand. A preferred adjuster should be capable of setting and maintaining any desirable angular adjustment in a sufficiently short time, independently of the respective torque acting on the camshaft. For this purpose, its working capacity or its adjusting capacity must be correspondingly large. In the case of feeding by the lubricating oil pump, problems occur at high oil temperature and also at low speed of the engine and hence of the pump, owing to the low oil pressure available. A high adjusting speed is desired. The required feed pressure and/or feed flow rate should be as low as possible. At the same time, the dimensions should be so small that no further design modifications on the engine are required. Preferably, the adjuster should be located radially inside the camshaft wheel and should be axially short.
A known adjuster uses an axially acting hydraulic piston for axial adjustment of a sleeve. The sleeve comprises an inner and an outer spiral gear, the two gears being formed with opposite pitches. The outer gear of the sleeve engages an inner gear firmly connected to the camshaft wheel, and the inner gear of the sleeve engages a gear connected to the camshaft. As a result of an axial adjustment of the sleeve, an angular adjustment is achieved between the camshaft wheel and the camshaft. Owing to the limited axial length, the adjustment range is limited. If the spiral angle is increased, the working piston must be enlarged in the case of an identical transmittable adjusting moment, which in turn leads to a larger piston diameter. Furthermore, the inevitable tooth play thus becomes more effective, which, owing to the periodically changing torques of the camshaft, leads to undesired noises and to increased wear. The oil actuating the hydraulic piston can flow in the wrong direction during torque peaks, particularly if, at low engine speed, the actuating oil pressure is lower than the compression pressure generated by the camshaft torque. In this way, the speed of adjustment and the accuracy of positioning are reduced. If this is to be avoided, the oil pump must be dimensioned substantially larger. Particularly at high engine speeds, this leads to higher energy losses. A further disadvantage of opposite spiral gears is their complicated production.
A further known adjuster is in the form of a so-called wing adjuster. An outer housing part is firmly connected to the camshaft wheel and comprises regions which project radially inward and divide an annular space into compartments. Wings project radially outward, each in a compartment, from a shaft part fastened to the camshaft. These wings rest tightly against the compartment border, laterally and radially on the outside, so that a rotary piston system is formed. By feeding oil to one side of all wings and discharging oil on the other side of all wings, it is possible to achieve a rotation of the outer housing part relative to the shaft part. By integration of the product of radius and operating pressure over the wing areas, a transmission and adjustment torque is determined. The more wings arranged on the circumference, the higher is the torque generated at a given oil pressure. At the same time, however, the maximum adjustment angle decreases in the case of a larger number of wings, because in fact the construction space in the circumferential direction is limited.
On starting the engine and possibly also at a high oil temperature, the oil pressure of the lubricating oil pump is too low to produce in the adjuster a torque which is greater than the maximum camshaft torques. The peaks of the camshaft torques adjust the rotational position of the adjuster until the wings rest against a compartment border. Because the camshaft torques oscillate between positive and negative maxima, the adjuster is deflected, at excessively low oil pressure, away from a desired rotational position alternately in the two directions of rotation until the wings make contact. This leads to considerable wear and to unpleasant noises. This undesired effect is reduced by using, for example, a brake element which damps the oscillating movements at low oil pressure.
For adjusting and maintaining the rotational position, an oil supply valve, a rotational position detector and a control are formed in such a way that deviations from a setpoint position are corrected by a corresponding valve actuation. The required oil pressure and correspondingly also the oil consumption of this rotary piston adjuster resulting from leakage are high because the full pressure is required also for maintaining a set rotational position or for transmitting the camshaft torques. Depending on the maximum camshaft torques occurring in both directions of rotation, high peak values occur in the working areas of the rotary piston system. If the oil supply valve is closed, these high compression pressures are troublesome only because correspondingly high leakage losses occur. When the adjusting valve is opened in the adjusting phase, the oil can flow in the wrong direction during torque peaks, because, particularly at low engine speed, the actuating oil pressure is lower than the compression pressure. In this way, the speed of adjustment and the accuracy of positioning are reduced so that, in such engines, the oil pump has to be dimensioned substantially larger. Particularly in the case of high engine speeds, this leads to higher energy losses.
It is the object of the invention to provide an adjuster which makes it possible to make any desirable angular adjustment even in the case of torques acting on the shaft, in particular in the case of the torque variation transmitted from the valves to the camshaft. Its working capacity and its adjusting capacity should be as large as possible even at low actuating fluid pressure. At the same time, the construction dimensions should be small and the production cost low.
This object is achieved by the features of claim 1. The dependent Claims describe alternative or advantageous embodiments.
In achieving the object, it was recognized that a hydrostatic rotary piston machine based on the orbit principle makes it possible to achieve the required adjusting capacity even at a low actuating oil pressure. Such machines comprise at least one stator, a rotor or rotary piston, a driven part and a valve device which connects rotating regions of the working area between stator and rotor to high and low pressure. Preferably, the number of teeth of the inner gear of the stator is one greater than that of the outer gear of the rotary piston. The individual components of a rotary piston machine can be produced at low cost, in particular by means of sintering. The annular machine parts and the working area require only little space. An adjuster according to the invention is preferably arranged directly between the camshaft and the camshaft wheel, the camshaft wheel in particular being formed directly on the stator so that only an extremely small additional construction space is required.
A further advantage is that any desired rotational position change or rotation between a shaft and a shaft wheel located thereon can be achieved. By forming the rotational position adjuster as a rotary piston machine or hydraulic motor having two annular rotational connections for feeding and removing hydraulic fluid, it can perform a drive function in other applications in addition to the adjusting function required, for example, in the case of camshafts. This means that the adjuster according to the invention can be used both as an orientation or positioning unit and as a movement unit on rotating shafts. In the most general case, the rotational position or rotary speed of the transmission wheel is changed relative to the shaft with hydraulic fluid which can be fed and removed via two annular rotational connections, for adjusting the phase position and/or the rotary speed of a shaft which can be caused to rotate by a drive shaft via a transmission device having at least one transmission wheel located on a shaft. For actuation, a fluid supply device comprising a control, a rotational position or rotary speed detector and at least one control valve is used, so that a setpoint rotational position or speed or acceleration can be set by a corresponding valve actuation.
If only the phase position of a camshaft is to be adjusted within a predetermined angular range, in particular a sufficiently large drive torque is required even in the case of low fluid or oil pressure. A rotary piston machine in which the transmission of rotation from the rotary piston to the driven part is effected with a speed ratio of 1:1 is preferably provided. The valve device of the rotary piston machine then preferably comprises first and second, radial valve channels which rotate with the driven part, in particular are formed thereon, are distributed uniformly over the circumference and cooperate with inner connection regions of radial stator channels distributed uniformly over the circumference. The outer connection regions of the stator channels open into the working area between the teeth of the inner gear of the stator. The number of first or second valve channels differs from the number of stator channels by one channel in each case, so that the inner connection regions of the stator channels are connected to first valve channels in a first circumferential segment and to second valve channels in a second circumferential segment. The first valve channels are connected via an inner annular channel in the driven part to one annular rotational connection, and the second valve channels are connected via a space between the driven part and the rotary piston and an outer connecting channel in the driven part to the other annular rotational connection.
To achieve a speed ratio of 1:1 between the rotary piston and the driven part, a force must be transmitted between the rotary piston, rotating eccentrically about the axis of the driven part, and the driven part. According to CH 676 490, the force or torque transmission can be effected, for example, by means of a cardan shaft. However, this would lead to a large construction length in the axial direction. A further transmission device mentioned in CH 676 490 comprises coupling by means of bolts which are held in matching holes in one part and, in the other part, in holes having diameters which are larger than the bolt diameters by twice the eccentricity. During the rotational transmission, the bolts roll along the border surfaces of the larger holes. This bolt transmission, too, leads to a greater construction length in the axial direction. A solution preferred owing to the short construction length and according to CH 676 490 comprises an inner gear on the rotary piston and an outer gear on the driven part. To ensure that the axis of rotation of a driven part driven by the rotary piston can be stationary, cooperating teeth are provided with tooth contours which are adapted to the existing eccentricity.
It has now been found that, on rotational transmission between rotary piston and driven part having an inner and an outer gear, a self-locking effect is achieved between the stator and the driven part. This means that a torque applied to the driven part is transmitted via the rotary piston to the stator. Because the rotary piston cannot be caused to rotate in practice, this is an essentially interlocking torque transmission which can be further increased by approximating the tooth contour to a triangular shape. The adjuster can thus be adjusted in its rotary angle position only by supplying oil pressure, but not by applying torque externally. It is thus ensured that high torque peaks of the camshaft cannot lead to high compression pressures in the working chambers of the hydraulic system and that no supporting pressure for torque transmission is required for normal operation, i.e. if no angular adjustment takes place. During the adjustment-free phases, essentially no oil leakage flows occur, which leads to a low mean oil throughput. Moreover, a reservoir could be filled with hydraulic oil during the adjustment-free phases, which is then available in adjustment phases. Consequently, the amount of hydraulic oil required by the oil pressure pump would be reduced, which reduces the requirements with respect to the pump and accordingly with respect to its power dissipation.
For adjusting the camshaft phase position, the adjuster is preferably arranged on the camshaft, but optionally on the drive shaft or on an additional transmission shaft.
The preferred adjusters operate according to the orbit principle of the high-torque hydraulic engines known in high-pressure hydraulics. This results in an extremely high working capacity. The rotational position adjustment is effected continuously and has no angular limitation. Because of the tooth shapes fitting one into the other and the self-locking produced in the preferred embodiments, no impact noises occur. In addition, the adjusters according to the invention are simple to produce and require only a few parts.
The embodiment mentioned above and described below with reference to the example and having a drive part which is rotatable at the speed of the rotary piston about a fixed axis and in particular comprises a control part of the valve device is a solution which can also be used as an advantageous, low-speed hydromotor. Of course, such a low-speed hydromotor can also be formed with a fixed driven part and rotating stator. It would then be possible to dispense with rotational connections. Low-speed hydromotors, in particular arranged on shafts, can advantageously be used, for example, as drives in machine tools.